Lighting fixtures having multiple lamps are generally known in the prior art for use in a variety of industries. In the entertainment industry, such lighting fixtures generally comprise a plurality of individual sealed beam PAR-type lamps placed in close proximity with each other and either set to a certain focus, made independently adjustable or made adjustable in groups. The individual lamps are usually arranged in a grid pattern comprising vertical and horizontal rows of lamp housings. Focusing the lamps may be achieved by individually panning and tilting the vertical and horizontal lamp rows, thereby providing rows of light which converge only on latitudinal and/or longitudinal planes dictated by the distance between the vertical and horizontal lamp rows. An example of a grid-type lighting fixture is shown in U.S. Pat. No. 5,473,523 to Von Fange, which discloses a plurality of lamps mounted on a movable platen such that the beam angle of all lamps may be simultaneously adjusted in the same direction to the same angle.
The inability of grid-type multiple lamp lighting fixtures to simultaneously focus the beam centers of each lamp on one point results in wasted foot candles and lacks efficiency. Even if the lamps are independently adjustable, it is difficult and time consuming to determine whether the lamps are focused on one point. Turning on a center lamp, projecting it onto a point and locking the pan and tilt positioning of the entire fixture also does not guarantee that the remaining lamps will be focused on the central point because there is no mechanism that maintains a constant relationship between all of the lamps.
Multiple lamp lighting fixtures of other configurations are also known in the art. For example, lighting fixtures having a plurality of lamps concentrically mounted around a central axis to pivot toward the axis are commonly used in the medical industry and are shown in U.S. Pat. Nos. 3,887,801 to Ilzig et al., 4,316,237 to Yamada et al. and 4,591,953 to Oram. U.S. Pat. No. 2,134,551 to Enfield shows a light projecting device having a fixed central lamp surrounded by a ring of lamps which may be adjustable. These patents show many different mechanical devices incorporated into lighting fixtures which adjust the inclination or angle of outer lamps to focus light beams at varying distances. However, the prior art has failed to provide a multiple lamp lighting fixture having a plurality of lamps concentrically mounted and pivotally hinged to a movable center hub or the preferred pivoting mechanism of this invention which provides simultaneous axial movement of a center hub and pivoting of the outer lamps. Such a lighting fixture is needed in the art to provide the convenience of an energy-efficient lighting fixture having a broad range of uses.
Moreover, prior art multiple-lamp lighting fixtures offer no provisions for mounting wire scrims or other devices which control the light output from a fixture without adversely affecting it. Wire scrims have been commonly used in the entertainment industry on single lamp lighting fixtures. The intensity of light emitted from known multiple-lamp lighting fixtures is generally controlled by varying the input voltage and/or selectively turning on or off individual lamps. However, adjusting the input voltage to the fixture often shifts the color temperature of the light emitted from the lamp (when measured in Kelvin units). Turning on or off individual lamps may also adversely affect the desired shape of the projected beam pattern.
It is therefore a broad object of this invention to provide an improved multiple lamp lighting fixture which may be used in a broad range of industries including entertainment, medicine, construction, emergency and other industrial applications.
A more specific object of the invention is to provide an energy efficient, multiple lamp lighting fixture capable of maximizing total light output from the fixture by simultaneously focusing the beam centers of all individual lamps onto one point anywhere along a central axis.
Another object of the invention is to provide a simple focusing mechanism that maintains a constant relationship between all lamps and permits all lamps to be adjusted in unison.
A still further object of the invention is to provide a multiple lamp lighting fixture having provisions for controlling light output without adversely affecting the color temperature of the light and without changing the shape of the projected light beam.